Methods and apparatuses for handling beam failure

ABSTRACT

Some embodiments of this disclosure provide a method performed by one or more transmission points, TRPs, for communicating with a user equipment, UE. In some embodiments, the method includes: using a first transmit, TX, beam to communicate with the UE; receiving, from the UE, information indicating that the UE has determined that the first TX beam has experienced a beam failure; and after the information is received, using a second TX beam to communicate with the UE.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/399,491, filed on Apr. 30, 2019 (published as US 2019-0261344 on Aug.22, 2019), which is a continuation of International Patent ApplicationNo. PCT/IB2017/056826, filed on Nov. 2, 2017 (published as WO2018/083624), which claims priority to U.S. Provisional PatentApplication No. 62/417,607, filed on Nov. 4, 2016. The above identifiedapplications and publications are incorporated by this reference.

TECHNICAL FIELD

Disclosed are embodiments for handling beam failure.

BACKGROUND

The next generation mobile wireless communication system, which isreferred to as “5G”, will support a diverse set of use cases and adiverse set of deployment scenarios. 5G will encompass an evolution oftoday's 4G networks and the addition of a new, globally standardizedradio access technology known as “New Radio” (NR).

The diverse set of deployment scenarios includes deployment at both lowfrequencies (100s of MHz), similar to LTE today, and very highfrequencies (mm waves in the tens of GHz). At high frequencies,propagation characteristics make achieving good coverage challenging.One solution to the coverage issue is to employ high-gain beamforming toachieve satisfactory link budget. With such high-gain beamforming, thebeams are typically quite narrow which makes beam trackingchallenging—i.e., finding, maintaining, and switching between suitablebeams as a UE moves both within and between the coverage areas ofmulti-beam transmission points (TRPs) (a.k.a., “transmit-receivepoints”).

Beamforming implies transmitting the same signal from multiple antennaelements of an antenna array with an amplitude and/or phase shiftapplied to the signal for each antenna elements. These amplitude/phaseshifts are commonly denoted as the antenna weights and the collection ofthe antenna weights for each of the antennas is a precoding vector.Different precoding vector give rise to a beamforming of the transmittedsignal and the weights can be controlled so that the signals arecoherently combining in a certain angle direction as seen from theantenna array in which case it is said that a beam is formed in thatdirection. If the antennas of the array are placed in two dimensions,i.e. in a plane, then the beam can be steered in both azimuth andelevation directions with respect to the plane perpendicular to theantenna array.

In 3GPP, at least two broad categories for beam handling have beenidentified for multi-beam systems: (1) connected mode mobility between abeam transmitted by a source (or serving) TRP and a beam transmitted bya target TRP, where the target is a TRP with which the UE has notestablished or maintained synchronization; and (2) beam management wherebeam tracking is required due to UE movement, and the beams aretypically transmitted by the same (serving) TRP with which the UEcontinually maintains time and frequency synchronization. Someembodiments of this disclosure apply to the latter procedure, i.e., beammanagement. In what follows, reference is made to a beam-pair link(BPL), which is defined as a pair of beams consisting of a suitabletransmit (TX) beam used by a TRP and a suitable receive (RX) beam usedby a UE for reliable transmission and reception.

Long Term Evolution (LTE) Radio Link Failure (RLF) Handling

In LTE, RLF declaration triggers a Radio Resource Control (RRC)connection re-establishment attempt, and this process works as follows.The UE continually monitors the “health” of an ongoing connection bymeasuring the signal-to-interference ratio (SINR) based on always-on,cell-specific reference signals (CRS). An RLF is declared by the UE ifthe UE deems that the radio conditions are poor enough that reliablereception of the Physical Downlink Control Channel (PDCCH) is notpossible. The “poor enough” criterion is controlled by at least 4parameters, thresholds Qout and Qin, an out-of-sync (OOS) count N310,and a timer T310 which are configured by higher layers. If the SINRmeasured on CRS falls below the threshold Qout on N310 consecutivemeasurement intervals, timer T310 is started. The threshold Qout istypically selected to correspond to a target block-error-rate (BLER) onthe PDCCH of 10%. If the measured SINR does not sufficiently improve(i.e., rise above the second threshold Qin) before T310 expires, thenthe UE declares and RLF. This triggers the RRC connectionre-establishment attempt—a higher layer, i.e., Layer 3 (RRC), definedprocess specified in the 3GPP Radio Resource Control specification36.331. It is similar to the sequence of steps which the UE goes throughin transitioning from RRC_IDLE to RRC_CONNECTED mode, except the corenetwork signaling is less in the case that the UE context has not beenflushed from the source base station (eNB) and/or the MobilityManagement Entity (MME).

The basic connection re-establishment steps start with the UE initiatinga cell search. Once the best cell (called the “target cell”) isdetermined the UE acquires system information from the broadcast channelof the target cell. The UE then begins a random access procedure (RACH)using RACH resources (time/frequency resources) specified in the systeminformation. Step 1 of the RACH procedure is for the UE to transmit aRACH preamble that is detectable by the target cell. Once the target eNBdetects the RACH preamble, it sends a random access response (RAR) inStep 2 acknowledging a successful preamble detection. In Step 3, the UEsends an “RRC Connection Re-establishment Request” message to the targeteNB. This triggers a set of procedures which may involve the target eNBto attempt a context fetch (information about the previous RRCconnection) from the original serving cell (called the “source cell”). Acontext fetch is required if the best cell determined by the UE cellsearch, i.e., the target cell, is different from the source cell. Thecontext fetch occurs over the X2 connection between the eNB hosting thetarget cell and the eNB hosting the source cell. If the context fetch issuccessful, the connection is re-established. If not, a brand new RRCconnection is setup which will involve further layer 3 (L3) procedures(e.g., RRC procedures) involving additional core network signaling.

Note that while the above radio link monitoring (RLM) procedures havenot yet been defined for 5G NR, it is expected that a similar mechanismwill be introduced with appropriate modifications for the new standard.

Reference Signals, antenna ports and quasi co-location (QCL)

In LTE, reference signals (RSs) used for channel estimation areequivalently denoted as antenna ports. Hence a UE can estimate thechannel from one antenna port by using the associated RS. One could thenassociate a certain data or control transmission with an antenna port,which is equivalent to say that the UE shall use the RS for that antennaport to estimate the channel used to demodulate the associated controlor data channel. One could also say that the data or control channel istransmitted using that antenna port.

In LTE, the concept of quasi-co location has been introduced in order toimprove the channel estimation performance when demodulating control ordata channels. The concept relies on that the UE could estimate longterm channel properties from one reference signal in order to tune itschannel estimation algorithm. For instance, the average channel delayspread can be estimated using one antenna port and used whendemodulating a data channel transmitted using another antenna port. Ifthis is allowed, it is specified that the first and second antenna portare quasi co-located (QCL) w.r.t average channel delay spread.

Hence, as used in LTE specifications, two antenna ports are “quasico-located” if the large-scale channel properties of the channel overwhich a symbol on one antenna port is conveyed can be inferred from thechannel over which a symbol on the other antenna port is conveyed. Thelarge-scale channel properties preferably include one or more of delayspread, Doppler spread, Doppler shift, average gain, and average delay.

In addition, or alternatively, the large-scale channel properties caninclude one or more of received power for each port, received timing(i.e., timing of a first significant channel tap), a number ofsignificant channel taps, and frequency shift. By performing channelestimation algorithm tuning based on the RSs corresponding to the quasico-located antenna ports, a quality of the channel estimation issubstantially improved.

In NR, it has been agreed to introduce QCL for spatial properties of thechannel on top of those QCL parameters use for LTE. By complementing theexisting QCL framework with new QCL parameters that depends on spatialchannel properties, one can allow a UE to perform spatial processingacross different signal types without violating the rule that a UE isnot allowed to use measurements from one reference signal to assist inthe reception or processing of another signal unless explicitlyspecified.

Examples of such spatial processing is analog receiver beamforming, andchannel estimation using spatial processing gain to improve the channelestimate.

Assume communication between two nodes in a network, a TX node and an RXnode. A TX node transmits a first set of reference signals (RS) from oneor multiple transmit antenna ports. A RX node receives the transmittedreference signals using one or multiple receive antenna ports anddetermines or estimates, based on the received first set of transmittedRS, one or more parameters capturing a spatial property of the channel.The RX node determines an indication that a second set of transmitted RSfrom one or multiple transmit antenna ports are quasi co-located (QCL)with the said first RS, where the QCL is given with respect to the oneor more parameters capturing a spatial property of the channel. The TXnode transmits the second set of transmit RS from one or multipletransmit antenna ports. The RX node utilizes one or more of thedetermined parameters capturing a spatial property of the channel thatis based on the first set of RS, to assist in the reception of thesecond set of RS.

In other words, the RX node, typically a UE can use the same RXbeamforming weights (a.k.a., antenna weights or “RX beam”) to receivethe second signals and associated RS (such as a control or a datatransmission DMRS) as the RX beamforming weights (“RX beam”) it usedwhen it received a first signal (for example a measurement signal, e.g.CSI-RS) if the second RS is QCL with the first RS with respect tospatial parameters.

A QCL parameter related to a spatial property is related to the UE RXbeamforming or UE RX reception parameters. Hence, if the UE use twodifferent spatial QCL parameters can indicate that the UE use twodifferent RX beamforming weights (or equivalently two different ways ofcombining the signals from the UE RX antennas).

Spatial parameters could be angle of arrival, angular spread or spatialcorrelation, spatial correlation matrix on the RX side or on the TXside.

It has been agreed for NR that information pertaining to UE-sidebeamforming/receiving procedure used for data reception can be indicatedthrough QCL to UE (from the 5G base station (denoted gNB)).

Mechanism(s) to address in NR beam failure and/or blockage are needed.

SUMMARY

In one aspect, there is provided a method performed by one or moretransmission points, TRPs, for communicating with a user equipment, UE.In some embodiments, the method includes: using a first transmit, TX,beam to communicate with the UE, receiving, from the UE, informationindicating that the UE has determined that the first TX beam hasexperienced a beam failure, and after the information is received, usinga second TX beam to communicate with the UE. In one embodiment, themethod further comprises: as a result of receiving the information fromthe UE, one of the TRPs transmitting a beam activation command informingthe UE that a TRP is or will be using the second TX beam to communicatewith the UE. In one embodiment, the method further comprises: as aresult of receiving the information from the UE, a first TRP using thefirst TX beam to transmit a first beam activation command informing theUE that the first TRP is or will be using the second TX beam tocommunicate with the UE and a second TRP using a second TX beam totransmit a second beam activation command informing the UE that thesecond TRP is or will be using the second TX beam to communicate withthe UE .

In another aspect, the method includes: using a first set of one or moreantenna ports as an active set of antenna ports for the UE, and, whilethe first set of antenna ports is being used as the active set ofantenna ports, receiving, from the UE, information indicating that theUE has determined that a TX beam associated with the first set ofantenna ports has experienced a beam failure. In some embodiments, thefirst set of antenna ports is one or multiple CSI-RS antenna ports. Insome embodiments, the method further comprises providing to the UEcertain parameters, wherein the certain parameters are configured suchthat the UE has a high probability of detecting a beam link failurebefore detecting a radio link failure (RLF). In some embodiments,wherein the information is a preamble. In some embodiments, receivingthe preamble from the UE comprises a TRP receiving a transmission fromthe UE on a random access channel, wherein the transmission includes thepreamble.

In another aspect, there is provided a TRP that includes: a transmitter,a receiver, a memory, and a data processing system comprising one ormore processors, wherein the TRP is configured to perform any of theabove described methods.

In another aspect, there is provided a method performed by a userequipment, UE, communicating with one or more transmission points, TRPs,wherein the one or more TRPs are configured to transmit information tothe UE using a first beam pair link, BPL, wherein the one or more TRPsuse the first BPL as an active BPL for the UE. The method includes: theUE determining whether the first BPL has experienced a beam failure,and, as a result of determining that the first BPL has experienced abeam failure, the UE transmitting a message indicating that the UE hasdetermined that the first BPL has experienced a beam failure. In someembodiments, the method of the message is a beam switch request. In someembodiments, the first BPL comprises a first receive, RX, beam and afirst transmit, TX, beam, and the method further comprises the UE usingthe first RX beam of the first BPL to receive a reference signaltransmitted by one or more of the TRPs using the first TX beam. In someembodiments, the method further comprises: the UE using a second RX beamof a second BPL to receive a reference signal transmitted by one or moreof the TRPs using a second TX beam. In some embodiments, the referencesignal is a channel state information reference signal, CSI-RS. In someembodiments, the method further comprises: after transmitting themessage, receiving from a TRP a message informing the UE that a TRP isor will be using a second BPL as the active BPL for the UE. In someembodiments, the method further comprises: after the UE transmits themessage, the UE using a second RX beam to search for a schedulingcommand transmitted to the UE. In some embodiments, the message is apreamble. In some embodiments, the preamble is distinguishable from thepreambles that the UE is configured to transmit when the UE is doing aRACH attempt. In some embodiments, transmitting the preamble comprisestransmitting the preamble using a random access channel.

In another aspect, there is provided a method performed by a userequipment, UE, communicating with one or more transmission points, TRPs,wherein the UE is measuring two sets of antenna ports, a first set and asecond set, transmitted from TRPs, wherein the TRPs use the first set ofantenna ports as an active set of antenna ports for the UE. In someembodiments, the method includes: the UE determining whether the firstset of antenna ports has experienced a beam failure, and, as a result ofdetermining that the first set of antenna ports has experienced a beamfailure, the UE transmitting a message indicating that the UE hasdetermined that the first set of antenna ports has experienced a beamfailure. In some embodiments, the message is a beam switch request. Insome embodiments, the first set of antenna ports comprises one or moreCSI-RS antenna ports. In some embodiments, the method further comprisesreceiving beam failure parameters, wherein the parameters are configuredsuch that the UE (101) has a high probability of detecting a beamfailure before detecting a radio link failure, RLF. In some embodiments,the message is a preamble.

In another aspect, there is provided a UE that includes: a transmitter,a receiver, a memory, and a data processing system comprising one ormore processors, wherein the UE is configured to perform any of theabove described methods.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate various embodiments.

FIGS. 1A, 1B and 1C illustrate the use of active and monitored BPLs forcommunications between a TRP and a UE.

FIG. 2 illustrates a beam link monitoring (BPLM) process.

FIG. 3 is a flow chart illustrating a process according to oneembodiment.

FIG. 4 is a flow chart illustrating a process according to oneembodiment.

FIG. 5 is a flow chart illustrating a process according to oneembodiment.

FIG. 6 is a flow chart illustrating a process according to oneembodiment.

FIG. 7 is a flow chart illustrating a process according to someembodiments.

FIG. 8 is a flow chart illustrating a process according to someembodiments.

FIG. 9 is a flow chart illustrating a process according to someembodiments.

FIG. 10 is a flow chart illustrating a process according to someembodiments.

FIG. 11 is a block diagram of a UE according to some embodiments.

FIG. 12 is a block diagram of TRP according to some embodiments.

FIG. 13 illustrates two TRPs communicating with a UE using different TXbeams.

DETAILED DESCRIPTION

According to some embodiments, one approach for robust beam managementin a multi-beam system is the maintenance of both an active BPL used forongoing transmission and reception of data and control signals, and amonitored BPL used for fallback (backup) purposes. Typically, both theactive and monitored BPLs are updated as the UE moves and new/betterBPLs are discovered. The maintenance of the BPLs can be achieved throughUE measurement and feedback to the TRP of the received quality(strength) of reference signals (RS) transmittedsemi-persistently/periodically from the TRP on different beams.Furthermore, the reference signal transmissions on a given TRP beam maybe repeated to allow the UE a chance to adjust/optimize its receive (RX)beam.

The maintenance of a monitored BPL may be important for robustcommunication in the case that the active BPL becomes blocked, either byan object that moves into the active BPL path or an object behind whichthe UE moves and becomes shadowed. Blocking is common at highfrequencies where penetration loss through objects is high anddiffraction around object edges is poor. When such blocking occurs (orother degradation of the quality of the link occurs) the event isreferred to as a “beam pair link failure” or BPLF or simply “beamfailure”. BPLF can occur either slowly/gradually or very suddenlydepending on the UE speed and the motion of objects in the environment.The narrower the beams, the more chance there is for sudden BPLFs tooccur. To recover from a BPLF on the active BPL, it may be desirable forthe TRP and UE to switch together to the monitored BPL. This process isillustrated in FIGS. 1A, 1B and 1C.

In FIG. 1A, there is shown a TRP 150 (e.g., a base station) using oneactive BPL for UE 101 to transmit to the UE control signaling and userdata and further using one monitored (backup) BPL for the UE. WhileFIGS. 1A, 1B, and 1C illustrate a single TRP communicating with the UE,in other embodiments two or more TRPs may be communicating with the TRP(see e.g., FIG. 13), wherein one of the TRPs (e.g., TRP 150) uses theactive BPL (e.g., uses a TX beam 102—i.e., certain antenna weights) tocommunicate with the UE and another of the TRPs (e.g., TRP 950) uses themonitored BPL (e.g., uses a TX beam 104) to communicate with the UE. Theactive BPL comprises active TX beam 102 and the corresponding active RXbeam 106, and the monitored BPL comprises the monitored TX beam 104 andthe corresponding monitored RX beam 108.

In FIG. 1B there is shown an object 190 that is blocking the active BPL,thereby causing the UE to detect a BPLF with respect to the active BPL(i.e., the active TX beam/active RX beam pair). A problem arises in thatthe TRP cannot switch to the monitored BPL since the UE is stillmonitoring the UE RX beam 106 corresponding to the active TX beam 102 asthe UE is unaware of the blocking. Moreover, the TRP may also be unwareof the blocking situation.

To restore the connection between the TRP and the UE, the TRP can usethe monitored BPL as the active BPL for the UE, as illustrated in FIG.1C. However, to efficiently perform this beam switching, the TRP mustfirst signal to the UE that it will start using the monitored BPL as theactive BPL, otherwise the UE will not know which UE RX beam to useduring reception (i.e., RX beam 106 or RX beam 108). This is problematicbecause the active BPL, which is used for control signaling, is blockedand has poor or non-existing channel quality. If the blocking happensslowly, there may be time to perform this signaling before the signaldegrades too much. There is a risk that the blocking will happen tooquickly such that the TRP does not have time to signal a “beam switch”(a.k.a., “BPL switch”) to the UE, and in this case the UE will continueto use the RX beam 106 corresponding to the TX beam 102 that is nowblocked.

Some embodiments of this disclosure provide a robust mechanism for BPLFrecovery through fallback to the monitored BPL, particularly in the casewhere sudden beam blockages occur. In this scenario, as described above,there may be no time for the TRP to send control messages over theactive BPL to tell the UE to switch to the monitored BPL. Likewise,there may be no time for the UE to provide BPL quality reports over theactive BPL to inform the TRP of a BPLF. The term BPLF is chosen since ata high level, BPLF has some similarities (but several key differences)to radio-link failure (RLF) in LTE today.

Two aspects to point out from the above discussion on radio linkmonitoring (RLM) are that (1) RRC Connection Re-establishment is a L3(RRC) procedure involving signaling between several nodes in the system(source eNB, target eNB, and potentially MME), and (2) the procedure asdefined today is a cell specific, rather than beam-oriented, procedure.

What is needed for in the context of beam-oriented systems for 5G NR isa robust and fast approach for switching between the active andmonitored BPLs in the case of a BPLF due to, e.g., a sudden blockage ofthe active BPL. This ensures that connection gaps as much as possibleare not observable by the end user. A key aspect for quick reaction toBPLF is to ensure that the switching process involves only L1 and/or L2signaling with a single TRP or at most between tightly synchronizedTRPs. While radio link monitoring with connection re-establishmenttriggered by RLF is suitable for catastrophic link failures, it is notsuitable for fast switching between an active BPL and a monitored BP dueto its relatively slow response times. Furthermore, radio linkmonitoring as defined today is not a beam-oriented process.

Some embodiments of this disclosure provide a low layer (L1/L2)mechanism for recovery from a beam pair link failure (BPLF) by enablingthe network (NW) to switch from an active BPL to a monitored (backup)BPL when the active BPL experiences a BPLF (e.g., quality of active BPLis below a threshold). The mechanism is intended to run in parallel withradio link monitoring which handles catastrophic link failures, but itoperates with faster response time allowing fast switching between theactive and monitored BPLs.

In one aspect, the mechanism is based on continuous UE monitoring of thequality of the active and monitored BPLs, and in the case that the UErecognizes a BPLF due to serious degradation of the active BPL, itnotifies the NW (i.e., transmits a signal). The notification is in formof a preamble, such as a specific RACH preamble, which is called a beampair link switch (BPS) preamble and which is distinct from those RACHpreambles used in the RRC Connection Re-establishment procedure. Animportant aspect of the BPS preamble is that the NW (e.g., TRP)understands that the BPS preamble is a UE requested (but still networkcontrolled) active/monitored beam switch request. Hence, the NW will notproceed with an RRC Connection Re-establishment procedure as a result ofreceiving the BPS preamble. As such, the network will not send a randomaccess response (RAR) in response to receiving the BPS preamble, norwill the NW expect a request for connection re-establishment from the UEbased on the BPS preamble.

An advantage of this is that the mechanism provides a very fast way ofinforming the NW that a beam pair link failure (BPLF) has occurred,facilitating a fast switch from the active BPL to the monitored BPLbefore a radio-link failure (RLF) is declared.

Some embodiments of this disclosure provide an approach for BPLmonitoring (BPLM). In an example embodiment, the BPLM includes thefollowing aspects: 1) continuous monitoring of the quality (e.g., signalstrength or signal-to-noise-and-interference ratio) of the active andmonitored BPL; 2) detection of BPLF based on the quality of at least theactive link; and 3) notification of BPLF to the network through thetransmission of a preamble transmission (e.g., a specific RACH preamble)called a beam link pair switch (BPS) preamble, which is distinct fromthose preambles used for either initial system access or RRCre-establishment request attempts. The BPS preamble transmission is tobe interpreted by the network as an active/monitored BPL switch request.

FIG. 2 shows that the BPLM process (inner loop) 202 can run in parallel(i.e., at the same time) as the radio link monitoring (RLM) process(outer loop) 204. The key difference is that BPLM is strictly a L1/L2process that whereas RLM involves L3 (RRC). As a result, BPLM isdesigned to have a faster reaction speed in terms of BPLF detection/BPLswitch than RLF detection/RRC connection re-establishment. As such, BPLswitch is meant to happen before the UE declares an RLF.

To enable BPLM, the UE is configured to measure the BPL quality, e.g.,signal strength or signal-to-noise-and-interference ratio, based oneither a UE specific or cell-specific reference signal (RS) that istransmitted on a per BPL basis. An example is the so-called channelstate information reference signal (CSI-RS) used in LTE today. A variantof this signal is expected to be standardized for 5G NR. Both the activeand monitored BPLs are updated as the UE moves within the coverage areaof one or more TRPs, based on, e.g., CSI-RSRP/RSRQ measurementscontinually fed back from the UE to the NW using the active BPL.

Based on these measurements and feedback reports, typically both the UEand the NW have a view of when or if the active BPL starts to degrade.This degradation can happen relatively slowly, or very suddenly. In theformer case, the NW typically has time to take action to switch theactive and monitored BPLs and communicate the switch to the UE. However,in the latter (more problematic) scenario, the UE may not have a chanceto feedback BPL quality reports to the network before the active BPL isbroken. In this case the network loses its ability to recognize if afailure has occurred, since the active BPL carrying the feedback reportsbecomes unusable.

Therefore, alternative mechanisms to inform the network of a beam pairlink failure (BPLF) are introduced.

Embodiment #1

In one embodiment, the BPLF indication mechanism makes use of a specialpreamble, called a BPL Switch (BPS) preamble. The UE is pre-configuredwith one or more BPS preambles by the NW such that the NW understandsthat when it receives a BPS preamble, the BPS preamble should beinterpreted as a beam pair link switch request rather than a RACHattempt or an RRC connection re-establishment request. Based onsuccessful BPS preamble detection, the NW switches the active andmonitored BPLs and begins transmission of data and/or control on themonitored BPL. The UE then searches for scheduling commands on the PDCCHusing the new active BPL (formerly the monitored BPL). Optionally, theNW may send an explicit “BPL activation” command informing the UE of theBPL switch, thus acting as a form of acknowledgement of the switchrequest.

The UE declaration of BPLF is based on, e.g., the event that theCSI-RSRP/RSRQ on the active BPL falls below a threshold Bout on Noutmeasurement occurrences. The threshold can be either an absolutethreshold, or a threshold relative to the monitored BPL. The parametersBout and Nout are pre-configured either through high layers (RRC) or bylower layers (L1/L2) on a more dynamic basis. Preferably, the Bout andNout parameters are chosen to ensure a high probability that the BPLFdeclaration occurs before the UE declares and RLF based on the Qout,Qin, N310, and T310 parameters.

Embodiment #2

In another embodiment, the UE declaration of beam pair link failure(BPLF) is based on the event that it has not successfully received aPDCCH for a pre-determined time Tout. The parameter Tout ispre-configured either through high layers (RRC) or by lower layers(L1/L2) on a more dynamic basis. Preferably, Tout is chosen to ensure ahigh probability that the BPLF declaration occurs before the UE declaresand RLF based on the Qout, Qin, N310, and T310 parameters.

Embodiment #3

In yet another embodiment, multiple BPS preambles are used and each BPSpreamble is transmitted in a different UE TX beam, i.e. the differenttransmissions are not mutually QCL with respect to spatial properties.In this way there can be a higher probability that the transmissionreaches a network node.

Embodiment #4

In yet another embodiment, the UE transmits the BPS preambles multipletimes in a specified order across different UE TX beams and at specifiedtime instants and frequency locations, wherein the order a certain UE TXbeam (or its spatial QCL parameter properties) are known by the networkso that the network (or TRP (e.g., gNB)) can use the corresponding RXbeams to receive the BPS preamble. For instance, the UE may transmit thefirst preamble in the UE TX beam corresponding to the active link, andthe second and third preamble in the UE TX beams corresponding to afirst and second monitored links respectively and so on. In this way theTRP can always direct its receive beam for each individual and expectedBPS preamble transmission from the UE since it knows which UE TX beam isassociated with a certain TRP RX beam.

Embodiment #5

In yet another embodiment, in case the UE does not get anacknowledgement of the switch request from the NW and the UE cannotdetect a PDCCH in the new UE RX beam (corresponding to the UE RX beamfrom the monitored BPL) there is a large chance that the NW did notdetect the BPS preamble. In this case it would be beneficial if the UEautomatically goes back to the old RX beam (corresponding to the activeBPL) after N (N configured by the network) number of slots in case theblocking disappeared and the NW is still using the active BPL.

Embodiment #6

In an embodiment in which the active BPL has experienced a BPLF but thefailure is not catastrophic (e.g., the active BPL is degraded, but notcompletely blocked), if the network receives the BPS preamble from theUE, the NW transmits the next PDCCH on both the active BPL and themonitored BPL along with a “BPL activation” command informing the UE ofa BPL switch. The two PDCCHs could be transmitted in OFDM symbols withsome time duration between (potentially within the same slot) such thatthe UE has time to switch UE RX beam and try to listen to both PDCCHsplus the “BPL activation” command. This increases the chances of gettingthe BPL switch command through to the UE. Once the switch command isreceived, the UE begins to use the monitored BPL.

FIG. 3 is a flow chart illustrating a process 300, according to someembodiments, that is performed by one or more transmission points (TRPs)for communicating with a user equipment (UE) and for recovering from abeam pair link failure (BPLF).

Process 300 may being in step s302 in which a first beam pair link (BPL)is used as an active BPL for the UE, wherein using the first BPLcomprises using a first TX beam. In step s304, a second a second BPL isused as a monitored BPL for the UE, wherein using the second BPLcomprises using a second TX beam. In step s306, while the first BPL isbeing used as the active BPL and the second BPL is being used as themonitored BPL: i) transmitting control information (e.g., a referencesignal) to the UE using the first BPL (e.g., using a first precodingvector) and ii) transmitting control information (e.g., a referencesignal) to the UE using the second BPL (e.g., using a second precodingvector). In step s308, a TRP receives, from the UE, a request (e.g., aBPL switch preamble) to start using the second BPL as the active BPL forthe UE. In step s310, after the request is received, a TRP uses thesecond BPL as the active BPL for the UE.

In some embodiments, process 300 further includes one of the TRPs, as aresult of receiving the request from the UE, transmitting a BPLactivation command informing the UE that a TRP is or will be using thesecond BPL as the active BPL for the UE.

In some embodiments, process 300 further includes a TRP, as a result ofreceiving the request from the UE, transmitting a first beam pairactivation command informing the UE that the TRP is or will be using thesecond BPL as the active BPL for the UE and a TRP transmitting a secondbeam pair activation command informing the UE that the TRP is or will beusing the second BPL as the active BPL for the UE, wherein the first BPLis used to transmit the first beam pair activation command to the UE,and the second BPL is used to transmit the second beam pair activationcommand to the UE.

In some embodiments, using the second BPL as the active BPL for the UEcomprises a TRP transmitting a scheduling command on a PDCCH to the UEusing the second BPL.

In some embodiments in which the request is a BPL switch preamble,receiving the BPL switch preamble from the UE comprises receiving atransmission from the UE on a random access channel, wherein thetransmission includes the BPL switch preamble, the BPL switch preambleis distinguishable from the preambles that the UE is configured totransmit when the UE is doing a RACH attempt, e.g., during a connectionsetup, a connection re-establishment, or a handover, and the TRP usesthe second BPL as the active BPL for the UE as a consequence ofreceiving the BPL switch preamble.

In some embodiments, the UE is configured to transmit the request usinga UE TX beam and the step of receiving the request from the UE comprisesa TRP using an RX beam corresponding to the UE TX beam to receive therequest.

FIG. 4 is a flow chart illustrating a process 400, according to someembodiments, that is performed by one or more transmission points (TRPs)for communicating with a user equipment (UE) and for recovering from abeam pair link failure (BPLF).

Process 400 may being in step s402 in which a first set of antenna portsis used as an active set of antenna ports for the UE. In step s404, asecond set of antenna ports is used as a monitored set of antenna portsfor the UE. In step s406, while the first set of antenna ports is beingused as the active set of antenna ports and the second set of antennaports is being used as the monitored set of antenna ports: i)transmitting control information (e.g., a reference signal) to the UEusing the first set of antenna ports and ii) transmitting controlinformation (e.g., a reference signal) to the UE using the second set ofantenna ports. In step s408, receiving, from the UE, a request (e.g. aBPL switch preamble) to start using the second set of antenna ports asthe active set of antenna ports for the UE. In step s410, after therequest is received, using the second set of antenna ports as the activeset of antenna ports for the UE. After the request is received, at leastone of the first set of antenna ports and a third set of antenna portsis used as a monitored set of antenna ports for the UE. In someembodiments, each set of antenna ports are transmitting using differentbeams. In some embodiments, a set of antenna ports is one or multipleCSI-RS antenna ports.

In some embodiments in which the request is a BPL switch preamble,receiving the BPL switch preamble from the UE comprises receiving atransmission from the UE on a random access channel, wherein thetransmission includes the BPL switch preamble, the BPL switch preambleis distinguishable from the preambles that the UE is configured totransmit when the UE is doing a RACH attempt, e.g., during a connectionsetup, a connection re-establishment, or a handover, and the TRP, as aconsequence of receiving the BPL switch preamble, uses the second set ofantenna ports as the active set of antenna ports for the UE.

In some embodiments, process 300 and 400 further includes providing tothe UE BPLF parameters (e.g., Bout, Nout, and Tout), wherein theparameters are configured such that the UE has a high probability ofdetecting a BPLF before detecting an RLF (based on, for example, Qin,Qout, N310, T310 etc.) (e.g., the BPLF parameters provided to the UE canbe configured such that Bout is not too low, or Nout is not too large incomparison to the RLF parameters).

FIG. 5 is a flow chart illustrating a process 500, according to someembodiments, that is performed by a user equipment (UE) communicatingwith one or more transmission points (TRPs), wherein the TRPs areconfigured to transmit information to the UE using a first beam pairlink (BPL), wherein the TRPs use the first BPL as an active BPL for theUE and use a second BPL as a monitored BPL for the UE, wherein the firstBPL comprises a first TX beam and a first RX beam corresponding to thefirst TX beam and the second BPL comprises a second TX beam and a secondRX beam corresponding to the second TX beam.

Process 500 may being in step s502 in which the UE uses the first RXbeam of the first BPL to receive a reference signal transmitted by a TRPto the UE using the first BPL. Using the first RX beam to receive asignal, in some embodiments, means that the UE uses certain parametersto receive the signal. For example, in some embodiments the UE usesphase and/or amplitude adjustment parameters for each signal receivedvia multiple receive antennas, which parameters are applied to thesignals before combining or summation of the signals. In step s504, theUE uses the second RX beam of the second BPL to receive a secondreference signal transmitted by a TRP to the UE using the second BPL. Instep s506, the UE determines whether the first BPL has experienced abeam pair link failure (BPLF). In step s508, the UE, as a result ofdetermining that the first BPL has experienced a BPLF, transmits to atleast one of the one or more TRPs a request to start using the secondBPL as the active BPL for the UE. In some embodiments, process 500 alsoincludes the UE, after transmitting the request, receiving from a TRP abeam pair activation command informing the UE that a TRP is or will beusing the second BPL as the active BPL for the UE.

In some embodiments, receiving the beam pair activation commandcomprises one of: the UE using the first RX beam to receive the beampair activation command, and the UE using the second RX beam to receivethe beam pair activation command.

In some embodiments, process 500 further includes, after the UEtransmits the request, the UE uses the second RX beam to search for ascheduling command transmitted to the UE.

In some embodiments, the request is a BPL switch preamble, the BPLswitch preamble is distinguishable from the preambles that the UE isconfigured to transmit when the UE is doing a RACH attempt, e.g., duringa connection setup, a connection re-establishment, or a handover, andtransmitting the BPL switch preamble comprises transmitting the preambleusing a random access channel.

In some embodiments, determining whether the first BPL has experienced aBPLF comprises: the UE calculating a reference signal quality value, andthe UE determining whether the calculated reference signal quality valuefalls below a threshold (Bout). In some embodiments, the threshold isdependent on the quality of the second BPL. In some embodiments,calculating the reference signal quality value comprises calculating oneor more of RSRP and RSRQ based on a first reference signal received bythe UE using the first RX beam.

In some embodiments, determining whether the first BPL has experienced aBPLF comprises: the UE calculating a plurality of reference signalquality values, and for each of the plurality of calculated referencesignal quality values, the UE determining whether the calculatedreference signal quality value (or a function thereof) is less than athreshold (Bout). In some embodiments, the UE determines whether thenumber of reference signal quality values that are less than thethreshold meets or exceeds a second threshold (Nout).

In some embodiments, determining whether the first BPL has experienced aBPLF comprises the UE determining that the UE has not successfullyreceived via the first BPL a PDCCH for a pre-determined time (Tout).

In some embodiments, as a result of determining that the first BPL hasexperienced a BPLF, the UE transmits a plurality of requests for theTRPs to start using the second BPL as the active BPL for the UE. Thetransmission of the plurality of requests may include: the UE using afirst UE TX beam to transmit a BLP switch preamble and the UE using asecond UE TX beam to transmit a BLP switch preamble, and the first andsecond UE TX beams are not mutually QCL with respect to spatialproperties.

FIG. 6 is a flow chart illustrating a process 600, according to someembodiments, that is performed by a user equipment (UE) communicatingwith one or more transmission points (TRPs), wherein the UE is measuringtwo sets of antenna ports, a first set and a second set, transmittedfrom TRPs, wherein the TRPs use the first set of antenna ports as anactive set of antenna ports for the UE and use a second set of antennaports as a monitored set of antenna ports for the UE.

Process 600 may begin in step s602 in which the UE estimates a qualityof the first set of antenna ports. In step s604, the UE estimates aquality of the second set of antenna ports. In step s606, the UEdetermines, using the estimated quality of the first set of antennaports, whether the first set of antenna ports has experienced a linkfailure. In step s608, as a result of determining that the first set ofantenna ports has experienced a link failure, the UE transmits to anyone or more of the TRPs a request for at least one of the TRPs to startusing the second set of antenna ports as the active set of antenna portsfor the UE.

In some embodiments, the first set of antenna ports are transmittingusing a first set of one or more beams, and the second set of antennaports are transmitting using a second set of one or more beams. In someembodiments, the first set of antenna ports comprises one or more CSI-RSantenna ports.

In some embodiments, process 600 further includes the UE receiving BPLFparameters (e.g., Bout, Nout, and Tout), wherein the parameters areconfigured such that the UE has a high probability of detecting a BPLFbefore detecting an RLF (based on, for example, Qin, Qout, N310, T310etc.) (e.g., the BPLF parameters provided to the UE can be configuredsuch that Bout is not too low, or Nout is not too large in comparison tothe RLF parameters).

In some embodiments, process 600 further includes, the UE, aftertransmitting the request, determining whether it has been unable todetect a PDCCH within N number of slots (N>1); and as a result ofdetermining that it has been unable to detect a PDCCH within N number ofslots, the UE reverts back to use a previous configuration for detectingPDCCHs.

In some embodiments, the request is a BPL switch preamble, the BPLswitch preamble is distinguishable from the preambles that the UE isconfigured to transmit when the UE is doing a RACH attempt, e.g., duringa connection setup, a connection re-establishment, or a handover, andtransmitting the BPL switch preamble comprises transmitting the preambleusing a random access channel.

FIG. 7 is a flow chart illustrating a process 700, according to someembodiments, that is performed by a TRP (e.g., TRP 150 or TRP 950). Instep s702, the TRP uses a first transmit, TX, beam to communicate withthe UE 101. In step s704, the TRP receives, from the UE, informationindicating that the UE has determined that the first TX beam hasexperienced a beam failure. In step s706, after the information isreceived, the TRP uses a second TX beam to communicate with the UE.

In some embodiments, the process 700 further includes, as a result ofreceiving the information from the UE, one of the TRPs transmitting abeam activation command informing the UE that a TRP is or will be usingthe second TX beam to communicate with the UE.

In some embodiments, the process 700 further includes, as a result ofreceiving the information from the UE, a first TRP using the first TXbeam to transmit a first beam activation command informing the UE thatthe first TRP is or will be using the second TX beam to communicate withthe UE and a second TRP using the second TX beam to transmit a secondbeam activation command informing the UE that the second TRP is or willbe using the second TX beam to communicate with the UE.

In some embodiments, using the second TX beam to communicate with the UEcomprises a TRP transmitting a scheduling command on a PDCCH to the UEusing the second TX beam.

In some embodiments, the received information indicating that the UE hasdetermined that the first TX beam has experienced a beam failure is apreamble. In some embodiments, receiving the preamble from the UEcomprises a TRP receiving a transmission from the UE on a random accesschannel, wherein the transmission includes the preamble. In someembodiments, the preamble is distinguishable from preambles that the UEis configured to transmit when the UE is doing a RACH attempt. In someembodiments, the TRP uses the second TX beam to communicate with the UEas a consequence of receiving the preamble.

In some embodiments, the process 700 further includes, before receivingthe information, i) transmitting a reference signal to the UE using thefirst TX beam and ii) transmitting the reference signal to the UE usingthe second TX beam.

In some embodiments, the received information indicating that the UE hasdetermined that the first TX beam has experienced a beam failure is abeam switch request.

FIG. 8 is a flow chart illustrating a process 800, according to someembodiments, that is performed by a TRP (e.g., TRP 150 or TRP 950). Instep s802, the TRP uses a first set of one or more antenna ports as anactive set of antenna ports for the UE 101. In step s804, the TRP, whilethe first set of antenna ports is being used as the active set ofantenna ports, receives, from the UE, information indicating that the UEhas determined that a TX beam associated with the first set of antennaports has experienced a beam failure.

In some embodiments, the first set of antenna ports is one or multipleCSI-RS antenna ports.

In some embodiments, the process further includes providing to the UEcertain parameters, wherein the certain parameters are configured suchthat the UE has a high probability of detecting a beam link failurebefore detecting a radio link failure (RLF).

In some embodiments, the received information is a preamble. In someembodiments, receiving the preamble from the UE comprises a TRPreceiving a transmission from the UE on a random access channel, whereinthe transmission includes the preamble. In some embodiments, thepreamble is distinguishable from the preambles that the UE is configuredto transmit when the UE is doing a RACH attempt, and the TRP uses asecond TX beam to communicate with the UE as a consequence of receivingthe preamble, wherein the second TX beam is associated with a second setof antenna ports.

FIG. 9 is a flow chart illustrating a process 900, according to someembodiments, performed by UE 101, which is communicating with a TRP,wherein the TRP is configured to transmit information to the UE using afirst beam pair link, BPL, wherein the TRP uses the first BPL as anactive BPL for the UE. In step s902, the UE 101 determines whether thefirst BPL has experienced a beam failure. In step s904, the UE, as aresult of determining that the first BPL has experienced a beam failure,transmits a message indicating that the UE has determined that the firstBPL has experienced a beam failure.

In some embodiments, the message is a beam switch request.

In some embodiments, the first BPL comprises a first receive, RX, beamand a first transmit, TX, beam. In some embodiments, the process furthercomprises the UE using the first RX beam of the first BPL to receive areference signal transmitted by one or more of the TRPs using the firstTX beam.

In some embodiments, the process further comprises the UE using a secondRX beam of a second BPL to receive a reference signal transmitted by oneor more of the TRPs using a second TX beam.

In some embodiments, the process further comprises, after transmittingthe message, receiving from a TRP a message informing the UE that a TRPis or will be using a second BPL as the active BPL for the UE.

In some embodiments, the process further comprises, after the UEtransmits the message, the UE uses a second RX beam to search for ascheduling command transmitted to the UE.

In some embodiments, the request is a preamble. In some embodiments, thepreamble is distinguishable from the preambles that the UE is configuredto transmit when the UE is doing a RACH attempt. In some embodiments,transmitting the preamble comprises transmitting the preamble using arandom access channel.

In some embodiments, determining whether the first BPL has experienced abeam failure comprises: the UE calculating a reference signal qualityvalue, and the UE determining whether the calculated reference signalquality value falls below a threshold.

In some embodiments, determining whether the first BPL has experienced abeam failure comprises: the UE calculating a plurality of referencesignal quality values based on measurements of reference signals, andfor each of the plurality of calculated reference signal quality values,the UE determining whether the calculated reference signal quality valueor a function thereof is less than a threshold.

In some embodiments, the process also includes determining whether thenumber of reference signal quality values that are less than thethreshold meets or exceeds a second threshold.

In some embodiments, as a result of determining that the first BPL hasexperienced a beam failure, the UE transmits a plurality of saidmessages.

FIG. 10 is a flow chart illustrating a process 1000, according to someembodiments, performed by the UE 101, wherein the UE is measuring twosets of antenna ports, a first set and a second set, transmitted fromone or more TRPs, wherein the first set of antenna ports is used as anactive set of antenna ports for the UE. In step s1002, the UE determineswhether the first set of antenna ports has experienced a beam failure.In step s1004, as a result of determining that the first set of antennaports has experienced a beam failure, the UE transmits a messageindicating that the UE has determined that the first set of antennaports has experienced a beam failure.

In some embodiments, wherein the message is a beam switch request.

In some embodiments, the first set of antenna ports comprises one ormore CSI-RS antenna ports.

In some embodiments, the process also includes the UE receiving beamfailure parameters, wherein the parameters are configured such that theUE has a high probability of detecting a beam failure before detecting aradio link failure, RLF.

In some embodiments, the message is a preamble. In some embodiments, thepreamble is distinguishable from the preambles that the UE is configuredto transmit when the UE is doing a RACH attempt.

In some embodiments, transmitting the preamble comprises transmittingthe preamble using a random access channel.

FIG. 11 is a block diagram of a UE 101 according to some embodiments. Asshown in FIG. 11, the UE may comprise: a data processing system (DPS)1102, which may include one or more processors 1155 (e.g., a generalpurpose microprocessor and/or one or more other processors, such as anapplication specific integrated circuit (ASIC), field-programmable gatearrays (FPGAs), and the like); a radio transmitter 1105 and a radioreceiver 1106 coupled to an antenna 1122 for use in wirelesslycommunicating with a radio access network (RAN) node (e.g., a TRP); andlocal storage unit (a.k.a., “data storage system”) 1112, which mayinclude one or more non-volatile storage devices and/or one or morevolatile storage devices (e.g., random access memory (RAM)). Inembodiments where the UE includes a general purpose microprocessor, acomputer program product (CPP) 1141 may be provided. CPP 1141 includes acomputer readable medium (CRM) 1142 storing a computer program (CP) 1143comprising computer readable instructions (CRI) 1144. CRM 1142 may be anon-transitory computer readable medium, such as, but not limited, tomagnetic media (e.g., a hard disk), optical media (e.g., a DVD), memorydevices (e.g., random access memory, flash memory), and the like. Insome embodiments, the CRI 1144 of computer program 1143 is configuredsuch that when executed by data processing system 1102, the CRI causesthe UE to perform steps described above (e.g., steps described abovewith reference to the flow charts). In other embodiments, the UE may beconfigured to perform steps described herein without the need for code.That is, for example, data processing system 1102 may consist merely ofone or more ASICs. Hence, the features of the embodiments describedherein may be implemented in hardware and/or software.

FIG. 12 is a block diagram of a TRP (e.g., TRP 150 or TRP 950) accordingto some embodiments. As shown in FIG. 12, the TRP may comprise: a dataprocessing system (DPS) 1202, which may include one or more processors1255 (e.g., a general purpose microprocessor and/or one or more otherprocessors, such as an application specific integrated circuit (ASIC),field-programmable gate arrays (FPGAs), and the like); a radiotransmitter 1205 and a radio receiver 1206 coupled to an antenna 1222for use in wirelessly communicating with a UE; and local storage unit(a.k.a., “data storage system”) 1212, which may include one or morenon-volatile storage devices and/or one or more volatile storage devices(e.g., random access memory (RAM)). In embodiments where the TRPincludes a general purpose microprocessor, a computer program product(CPP) 1241 may be provided. CPP 1241 includes a computer readable medium(CRM) 1242 storing a computer program (CP) 1243 comprising computerreadable instructions (CRI) 1244. CRM 1242 may be a non-transitorycomputer readable medium, such as, but not limited, to magnetic media(e.g., a hard disk), optical media (e.g., a DVD), memory devices (e.g.,random access memory, flash memory), and the like. In some embodiments,the CRI 1244 of computer program 1243 is configured such that whenexecuted by data processing system 1202, the CRI causes the TRP toperform steps described above (e.g., steps described above withreference to the flow charts). In other embodiments, the TRP may beconfigured to perform steps described herein without the need for code.That is, for example, data processing system 1202 may consist merely ofone or more ASICs. Hence, the features of the embodiments describedherein may be implemented in hardware and/or software.

Additional Embodiments TRP Embodiments

1. A method performed by one or more transmission points (TRPs) forcommunicating with a user equipment (UE) and for recovering from a beampair link failure (BPLF), the method comprising: using a first beam pairlink (BPL) as an active BPL for the UE, wherein using the first BPLcomprises using a first TX beam; using a second BPL as a monitored BPLfor the UE, wherein using the second BPL comprises using a second TXbeam; while the first BPL is being used as the active BPL and the secondBPL is being used as the monitored BPL: i) transmitting controlinformation (e.g., a reference signal) to the UE using the first BPL andii) transmitting control information (e.g., a reference signal) to theUE using the second BPL; receiving, from the UE, a request to startusing the second BPL as the active BPL for the UE; and after the requestis received, using the second BPL as the active BPL for the UE.

2. The method of embodiment 1, further comprising: as a result ofreceiving the request from the UE, one of the TRPs transmitting a BPLactivation command informing the UE that a TRP is or will be using thesecond BPL as the active BPL for the UE.

3. The method of embodiment 1, further comprising: as a result ofreceiving the request from the UE, a TRP transmitting a first beam pairactivation command informing the UE that the TRP is or will be using thesecond BPL as the active BPL for the UE and a TRP transmitting a secondbeam pair activation command informing the UE that the TRP is or will beusing the second BPL as the active BPL for the UE, wherein the first BPLis used to transmit the first beam pair activation command to the UE,and the second BPL is used to transmit the second beam pair activationcommand to the UE.

4. The method of any one of embodiments 1-3, wherein using the secondBPL as the active BPL for the UE comprises a TRP transmitting ascheduling command on a PDCCH to the UE using the second BPL.

5. The method of any one of embodiments 1-4, wherein the request is aBPL switch preamble.

6. The method of embodiment 5, wherein receiving the BPL switch preamblefrom the UE comprises receiving a transmission from the UE on a randomaccess channel, wherein the transmission includes the BPL switchpreamble, the BPL switch preamble is distinguishable from the preamblesthat the UE is configured to transmit when the UE is doing a RACHattempt, e.g., during a connection setup, a connection re-establishment,or a handover, and the TRP uses the second BPL as the active BPL for theUE as a consequence of receiving the BPL switch preamble.

7. The method of any one of embodiments 1-6, wherein the UE isconfigured to transmit the request using a UE TX beam and the step ofreceiving the request from the UE comprises a TRP using an RX beamcorresponding to the UE TX beam to receive the request.

8. A method performed by one or more transmission points (TRPs) forcommunicating with a user equipment (UE) and for recovering from a beampair link failure (BPLF), the method comprising: using a first set ofantenna ports as an active set of antenna ports for the UE; using asecond set of antenna ports as a monitored set of antenna ports for theUE; while the first set of antenna ports is being used as the active setof antenna ports and the second set of antenna ports is being used asthe monitored set of antenna ports: i) transmitting control information(e.g., a reference signal) to the UE using the first set of antennaports and ii) transmitting control information (e.g., a referencesignal) to the UE using the second set of antenna ports; receiving, fromthe UE, a request to start using the second set of antenna ports as theactive set of antenna ports for the UE; and after the request isreceived, using the second set of antenna ports as the active set ofantenna ports for the UE.

9. The method of embodiment 8, further comprising, after the request isreceived, using at least one of the first set of antenna ports and athird set of antenna ports as a monitored set of antenna ports for theUE

10. The method of any one of embodiments 8-9, wherein each set ofantenna ports are transmitting using different beams.

11. The method of any one of embodiments 8-9, wherein a set of antennaports is one or multiple CSI-RS antenna ports.

12. The method of any one of embodiments, 1-11, further comprisingproviding to the UE BPLF parameters (e.g., Bout, Nout, and Tout),wherein the parameters are configured such that the UE has a highprobability of detecting a BPLF before detecting an RLF (based on, forexample, Qin, Qout, N310, T310 etc.) (e.g., the BPLF parameters providedto the UE can be configured such that Bout is not too low, or Nout isnot too large in comparison to the RLF parameters).

13. The method of any one of embodiments 8-12, wherein the request is aBPL switch preamble.

14. The method of embodiment 13, wherein receiving the BPL switchpreamble from the UE comprises receiving a transmission from the UE on arandom access channel, wherein the transmission includes the BPL switchpreamble, the BPL switch preamble is distinguishable from the preamblesthat the UE is configured to transmit when the UE is doing a RACHattempt, e.g., during a connection setup, a connection re-establishment,or a handover, and the TRP uses the second set of antenna ports as theactive set of antenna ports for the UE as a consequence of receiving theBPL switch preamble.

15. A TRP comprising a transmitter, a receiver, a memory, and a dataprocessing system comprising one or more processors, wherein the TRP isconfigured to perform the method of any one of embodiments 1-14. UEEmbodiments

16. A method performed by a user equipment (UE) communicating with oneor more transmission points (TRPs), wherein the TRPs are configured totransmit information to the UE using a first beam pair link (BPL),wherein the TRPs use the first BPL as an active BPL for the UE and use asecond BPL as a monitored BPL for the UE, wherein the first BPLcomprises a first TX beam and a first RX beam corresponding to the firstTX beam and the second BPL comprises a second TX beam and a second RXbeam corresponding to the second TX beam, the method comprising: the UEusing the first RX beam of the first BPL to receive a reference signaltransmitted by a TRP to the UE using the first BPL; the UE using thesecond RX beam of the second BPL to receive a second reference signaltransmitted by a TRP to the UE using the second BPL; the UE determiningwhether the first BPL has experienced a beam pair link failure (BPLF);and as a result of determining that the first BPL has experienced aBPLF, the UE transmitting to at least one of the one or more TRPs arequest to start using the second BPL as the active BPL for the UE.

17. The method of embodiment 16, further comprising: after transmittingthe request, receiving from a TRP a beam pair activation commandinforming the UE that a TRP is or will be using the second BPL as theactive BPL for the UE.

18. The method of embodiment 17, wherein receiving the beam pairactivation command comprises one of: the UE using the first RX beam toreceive the beam pair activation command, and the UE using the second RXbeam to receive the beam pair activation command.

19. The method of any one of embodiments 16-18, further comprising:after the UE transmits the request, the UE using the second RX beam tosearch for a scheduling command transmitted to the UE.

20. The method of any one of embodiments 16-19, wherein the request is aBPL switch preamble, the BPL switch preamble is distinguishable from thepreambles that the UE is configured to transmit when the UE is doing aRACH attempt, e.g., during a connection setup, a connectionre-establishment, or a handover, and transmitting the BPL switchpreamble comprises transmitting the preamble using a random accesschannel.

21. The method of any one of embodiments 16-20, wherein determiningwhether the first BPL has experienced a BPLF comprises: the UEcalculating a reference signal quality value, and the UE determiningwhether the calculated reference signal quality value falls below athreshold (Bout).

22. The method of embodiment 21, wherein the threshold is dependent onthe quality of the second BPL.

23. The method of any one of embodiments 18-22, wherein calculating thereference signal quality value comprises calculating one or more of RSRPand RSRQ based on a first reference signal received by the UE using thefirst RX beam.

24. The method of any one of embodiment 18-23, wherein determiningwhether the first BPL has experienced a BPLF comprises: the UEcalculating a plurality of reference signal quality values, and for eachof the plurality of calculated reference signal quality values, the UEdetermining whether the calculated reference signal quality value (or afunction thereof) is less than a threshold (Bout).

25. The method of embodiment 24, further comprising determining whetherthe number of reference signal quality values that are less than thethreshold meets or exceeds a second threshold (Nout).

26. The method of any one of embodiments 16-20, wherein determiningwhether the first BPL has experienced a BPLF comprises the UEdetermining that the UE has not successfully received via the first BPLa PDCCH for a pre-determined time (Tout).

27. The method of any one of embodiments 16-20, wherein, as a result ofdetermining that the first BPL has experienced a BPLF, the UE transmitsa plurality of requests for the TRPs to start using the second BPL asthe active BPL for the UE, transmitting the plurality of requestscomprises: the UE using a first UE TX beam to transmit a BLP switchpreamble and the UE using a second UE TX beam to transmit a BLP switchpreamble, and the first and second UE TX beams are not mutually QCL withrespect to spatial properties.

28. A method performed by a user equipment (UE) communicating with oneor more transmission points (TRPs), wherein the UE is measuring two setsof antenna ports, a first set and a second set, transmitted from TRPs,wherein the TRPs use the first set of antenna ports as an active set ofantenna ports for the UE and use a second set of antenna ports as amonitored set of antenna ports for the UE, the method comprising: the UEestimates a quality of the first set of antenna ports; the UE estimatesa quality of the second set of antenna ports; the UE determining, byusing the estimated quality of the first set of antenna ports, whetherthe first set of antenna ports has experienced a link failure; and as aresult of determining that the first set of antenna ports hasexperienced a link failure, the UE transmitting to any one or more ofthe TRPs a request for at least one of the TRPs to start using thesecond set of antenna ports as the active set of antenna ports for theUE.

29. The method of embodiment 28, wherein the first set of antenna portsare transmitting using a first set of one or more beams, and the secondset of antenna ports are transmitting using a second set of one or morebeams.

30. The method of any one of embodiments 28-29, wherein the first set ofantenna ports comprises one or more CSI-RS antenna ports.

31. The method of any one of embodiments 16-30, further comprisingreceiving BPLF parameters (e.g., Bout, Nout, and Tout), wherein theparameters are configured such that the UE has a high probability ofdetecting a BPLF before detecting an RLF (based on, for example, Qin,Qout, N310, T310 etc.) (e.g., the BPLF parameters provided to the UE canbe configured such that Bout is not too low, or Nout is not too large incomparison to the RLF parameters).

32. The method of any one of embodiments 16-31, further comprising:after transmitting the request, the determines whether it has beenunable to detect a PDCCH within N number of slots (N>1); and as a resultof determining that it has been unable to detect a PDCCH within N numberof slots, the UE reverts back to use a previous configuration fordetecting PDCCHs.

33. The method of any one of embodiments 28-32, wherein the request is aBPL switch preamble, the BPL switch preamble is distinguishable from thepreambles that the UE is configured to transmit when the UE is doing aRACH attempt, e.g., during a connection setup, a connectionre-establishment, or a handover, and transmitting the BPL switchpreamble comprises transmitting the preamble using a random accesschannel.

34. A UE comprising a transmitter, a receiver, a memory, and a dataprocessing system comprising one or more processors, wherein the UE isconfigured to perform the method of any one of embodiments 16-33.

Additional Disclosure

The text that follows is based on the material from the appendix filedwith U.S. Provisional Application No. 62/417,607, filed on Nov. 4, 2016,to which this application claims priority:

Title: On robust beam management

Agenda Item: 7.1.3.3

Document for: Discussion and Decision

1. Introduction

In RAN1#86bis, the following agreements were made:

Agreements:

1) NR supports mechanism(s) in the case of link failure and/or blockagefor NR (whether to use new procedure is FFS)

2) Study at least the following aspects: a) Whether or not an DL or ULsignal transmission for this mechanism is needed (e.g., RACH preamblesequence, DL/UL reference signal, control channel, etc.); and b) ifneeded, resource allocation for this mechanisms (e.g., RACH resourcecorresponding mechanism, etc.)

In this disclosure, the need of multiple beam pair links and how tohandle beam pair link failures is discussed.

2. Discussion

Narrow beam transmission and reception schemes will be needed at higherfrequencies to compensate the high propagation loss. For a givencommunication link, a beam can be applied at both the TRP and the UE,which will be referred to as a beam pair link (BPL) in thiscontribution. The task of the beam management procedure is to discoverand maintain beam pair links.

In the example of FIG. 13, two BPLs have been discovered and are beingmaintained by the network. Note that even in the case of a single TRP,multiple BPLs are still possible, considering reflections etc. A BPL isdiscovered and monitored by the network using measurements, eitheruplink measurements using uplink sounding or downlink measurements usingthe reference signals used for beam management, i.e., CSI-RS.

Due to the high penetration loss through objects and poor diffractionaround object edges at high frequencies a BPL will be sensitive toblocking. Blocking can occur either slowly/gradually or very suddenlydepending on the UE speed and the motion of objects in the environment.The narrower the beams, the more chance there is for sudden blocking tooccur. To establish more robust communication in a multi-beam system,multiple BPLs can be used between a TRP (or multiple TRPs) and a UE.There can be one or more active BPL(s) used for ongoing transmission andreception of data and control signals, and one or more monitored BPL(s)used for backup purposes.

It is therefore believed that it may be useful to monitor multiple BPLsin parallel for a given UE:

-   -   Robustness is achieved since a BPL may suddenly be blocked and        control and data transmission can quickly be carried over to the        alternative BPL    -   Distributed MIMO transmissions can be supported by using SU-MIMO        transmissions to the UE from multiple TRPs at the same time        -   In LOS conditions, the rank per BPL is limited to two (dual            polarizations) while distributed MIMO allows for higher rank            transmissions.

In the case one or multiple BPL are used simultaneously for a UE, and incase of multiple BPLs it is useful to introduce some priority, e.g. forPDCCH search space monitoring purpose. Hence, the notion of active andmonitored BPL where the UE monitors the PDCCH assuming at least theactive BPL while the monitored BPLs are maintained to serve as a backupor to discover new BPLs. Hence, measurements are scheduled for each BPLseparately for beam refinement or beam discovery, where discovery ismore targeted the monitored link is introduced.

The TRP can switch active BPL to a monitored BPL by signaling a BPLswitch command to the UE. In case the TRP notice a slow blocking of aBPL the TRP can signal a BPL switch command, through the active BPL, tothe UE such that the monitored BPL becomes the new active BPL. However,in case the blocking is too sudden the TRP will not have time to signala BLP switch command to the UE and the link used for control and datasignals between TRP and UE will be lost. When such blocking occurs, theevent can be referred to as a “beam pair link failure” or BPLF or “beamfailure”. There is a need for NR to handle BPLF in a quick and efficientway to maintain high and reliable performance for the users.

Observation 1: Using multiple beam-pair links can improve the robustnessin beam-based systems

Proposal 1: An active beam pair link is supported for which the UE ismonitoring PDCCH

Proposal 2: One or more monitored beam-pair links is supported toimprove the robustness and to discover new links

Observation 2: There is a need to handle BPL failure in a quick andefficient way to maintain high and reliable performance for the users.

One way to mitigate BPLF is for the UE to receive the DL controlsignaling (PDCCH) over both the active and monitored BPLs but with alarger duty cycle for the monitored BPL compared to the active BPL. Forexample, the control signaling can be scheduled every slot on the activelink and scheduled every Nth slot on the monitored link. In this way, incase the active BPL is blocked and the UE cannot decode the controlsignaling, the UE can receive control signaling transmitted on themonitored link.

Proposal 3: Study PDCCH reception on monitored BPLs as a mean forincrease robustness against BPL blocking.

The control signaling on the monitored link can contain a BPL switchcommand, to change the used BPL as being active.

The handling of active and monitored BPLs, as well as discovering newBPLs, should be controlled by the network as much as possible. However,in some cases when a BPLF has occurred it might be difficult for thenetwork to re-establish the connection, i.e. find a new suitable BPLbetween the TRP and the UE. If the BPLF last too long it will cause aradio link failure (RLF), which introduce extra latency and overheadsignaling.

It has been discussed that the UE could signal to the TRP that a BPLFhas occurred using a specific RACH preamble and in this way help thenetwork to find a new BPL quicker. The specific RACH preamble can bededicated for handling BPLFs, such that the network knows that when thisRACH preamble is detected a BPLF has occurred.

Proposal 4: The handling of active and monitored BPLs, as well aspotential BPLFs, should be controlled by the network as much as possible

3. Conclusions

In this disclosure, the following observations are noted:

Observation 1: Using multiple beam-pair links can improve the robustnessin beam-based systems

Observation 2: There is a need to handle BPL failure in a quick andefficient way to maintain high and reliable performance for the users.

Based on aspects discussed in this disclosure, the following areproposed, along with other disclosed embodiments:

Proposal 1: An active beam pair link is supported for which the UE ismonitoring PDCCH

Proposal 2: One or more monitored beam-pair links are supported toimprove the robustness and to discover new links

Proposal 3: Study PDCCH reception on monitored BPLs as a means toincrease robustness against BPL blocking.

Proposal 4: The handling of active and monitored BPLs, as well aspotential BPLFs, should be controlled by the network as much as possible

While various embodiments of the present disclosure are describedherein, it should be understood that they have been presented by way ofexample only, and not limitation. Thus, the breadth and scope of thepresent disclosure should not be limited by any of the above-describedexemplary embodiments. Moreover, any combination of the above-describedelements in all possible variations thereof is encompassed by thedisclosure unless otherwise indicated herein or otherwise clearlycontradicted by context.

Additionally, while the processes described above and illustrated in thedrawings are shown as a sequence of steps, this was done solely for thesake of illustration. Accordingly, it is contemplated that some stepsmay be added, some steps may be omitted, the order of the steps may bere-arranged, and some steps may be performed in parallel.

1. A user equipment (UE), the UE comprising: a transmitter; a receiver;a memory; and a data processing system comprising one or moreprocessors, wherein the UE is adapted to: based on measurements ofreference signals that were transmitted using a first transmit (TX)beam, detect whether a beam failure has occurred; and as a direct resultof detecting that the beam failure has occurred, transmit at least afirst beam failure message indicating that the UE has detected that thebeam failure has occurred.
 2. The UE of claim 1, wherein the first beamfailure message is a preamble.
 3. The UE of claim 2, whereintransmitting the preamble comprises transmitting the preamble using arandom access channel (RACH), and the preamble is not a handoverpreamble.
 4. The UE of claim 3, wherein the preamble is distinguishablefrom preambles that the UE is configured to transmit when the UE isdoing a RACH attempt.
 5. The UE of claim 1, wherein the UE is configuredsuch that, as a result of the UE detecting that the beam failure hasoccurred, the UE transmits not only the first beam failure message butalso at least a second beam failure message that also indicates that theUE has detected that the beam failure has occurred.
 6. The UE of claim1, wherein the UE is configured to use a first receive (RX) beam toreceive the reference signals.
 7. The UE of claim 6, wherein thereference signals are a channel state information reference signals(CSI-RSs).
 8. The UE of claim 6, wherein the UE is further configuredsuch that, after the UE transmits the first beam failure messageindicating that the UE has determined that the beam failure hasoccurred, the UE uses a second RX beam to search for a schedulingcommand transmitted to the UE.
 9. The UE of claim 1, wherein the UE isconfigured to detect whether the beam failure has occurred by performinga process that comprises: the UE determining a radio link quality value,and the UE determining whether the determined radio link quality valuefalls below a threshold.
 10. The UE of claim 1, wherein the UE isconfigured to detect whether the beam failure has occurred by performinga process that comprises: the UE determining a plurality of radio linkquality values based on the measurements, and for each of the pluralityof determined radio link quality values, the UE comparing the determinedradio link quality value, or a function thereof, to a first threshold.11. The UE of claim 10, wherein the process further comprisesdetermining whether the number of radio link quality values that areless than the first threshold meets or exceeds a second threshold.
 12. Amethod performed by a user equipment (UE), the method comprising: basedon measurements of reference signals that were transmitted using a firsttransmit (TX) beam, the UE detecting that a beam failure has occurred;and as a direct result of detecting that the beam failure has occurred,the UE transmitting a beam failure message indicating that the UE hasdetected that the beam failure has occurred.
 13. The method of claim 12,further comprising: after transmitting the beam failure message,receiving a message informing the UE that a serving base station hasselected a new TX beam for use in communicating with the UE.
 14. Anetwork node, the network node comprising: a transmitter; a receiver; amemory; and a data processing system comprising one or more processors,wherein the network node is adapted to: use a first transmit (TX) beamto communicate with a user equipment (UE); receive, from the UE, beamfailure information indicating that the UE has detected that beamfailure has occurred; and after receiving the beam failure information,use a second TX beam to communicate with the UE.
 15. The network node ofclaim 14, wherein the beam failure information is a preamble.
 16. Thenetwork node of claim 15, wherein the preamble is received via a randomaccess channel.
 17. The network node of claim 15, wherein the preambleis distinguishable from preambles that the UE is configured to transmitwhen the UE performs a random access channel (RACH) attempt.
 18. Thenetwork node of claim 15, wherein the network node is further adaptedsuch that, as a consequence of receiving the preamble, the network nodeuses the second TX beam to communicate with the UE.
 19. The network nodeof claim 15, wherein the network node is further adapted such that, as aconsequence of receiving the preamble, the network node uses the secondTX beam to transmit to the UE a scheduling command on a physicaldownlink control channel (PDCCH).
 20. The network node of claim 14,wherein the network node is further adapted to transmit a beamactivation command as a result of receiving the beam failureinformation, the beam activation command informing the UE that second TXbeam will be used to communicate with the UE.